Predictive modelling of hydraulic head responses to dipole flow experiments in a fractured/karstified limestone aquifer: Insights from a comparison of five modelling approaches to real-field experiments
Résumé
Five modelling approaches were tested against a well-studied limestone aquifer constituting the Hydrogeological Experimental Site (HES) of Poitiers, France. The modelling exercise consisted of predicting the drawdown responses of a series of observation wells for two dipole (pumping-injection) flow experiments involving two distinct well pairs at the HES. The differences between model predictions appear to be mainly related to the hydraulic datasets used for model parameterisation and, to a much lesser extent, to the conceptual modelling approach (equivalent porous medium vs. discrete fracture networks), the model dimensionality (two-dimensional vs. three-dimensional), and/or the parameterisation approach (forward vs. inverse). Despite the abundance and diversity of calibration/parameterisation data, all of the models failed to predict the drawdowns with a reasonable degree of accuracy. Only the order of magnitude of the drawdowns was correctly predicted by three of the five models, whereas all models failed to predict the drawdown behaviour at both intermediate and late times. The primary source of error is attributed to a lack of information in the single-well pumping test data, which did not capture the multi-permeability structure of the aquifer as revealed a posteriori by the responses to dipole flow experiments. This highlights the need to develop novel (or improved) approaches to characterise the hydraulic properties of limestone aquifers.